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Stewart's theory and acid-base changes induced by crystalloid infusion in humans: a randomized physiological trial
Antonio Maria Dell'Anna1, Domenico Luca Grieco2, Cristina Dominedò1
1Department of Anesthesia and Intensive Care Medicine, Fondazione Policlinico Universitario "A. Gemelli" IRCCS, Università Cattolica del Sacro Cuore, L.Go F. Vito, 00168, Rome, Italy.
Annals of Intensive Care
|April 22, 2025
Summary
High chloride crystalloids like normal saline lower plasma pH by reducing the strong ion difference, causing acidosis. Lactated Ringer's and Crystalsol maintain pH better due to lower chloride content.
Area of Science:
- Anesthesiology
- Intensive Care Medicine
- Renal Physiology
Background:
- Stewart's acid-base theory explains pH changes from crystalloid infusion via strong ion difference and weak acid concentration.
- Previous human studies assessing renal response and hemodilution effects during crystalloid infusion are limited.
- This study evaluates Stewart's acid-base approach in humans receiving crystalloid infusions.
Purpose of the Study:
- To investigate the effects of different crystalloid solutions on plasma pH in surgical patients.
- To assess the validity of Stewart's acid-base theory in the context of crystalloid infusion.
- To compare the impact of normal saline, lactated Ringer's, and Crystalsol on acid-base balance and electrolytes.
Main Methods:
- A randomized trial involving 45 surgical patients with minimal blood loss.
- Patients received 10 ml/kg of normal saline, lactated Ringer's, or Crystalsol, followed by 20 ml/kg after 2 hours.
- Plasma and urinary acid-base parameters and electrolytes were measured, with pH one hour after the second bolus as the primary endpoint.
Main Results:
- Normal saline administration resulted in significantly lower pH (7.34) compared to lactated Ringer's (7.40) and Crystalsol (7.42) one hour after the second fluid bolus.
- The saline group received more chloride and experienced a greater increase in plasma chloride concentration over time.
- While overall urinary chloride excretion was similar, the saline group showed higher urinary chloride concentration and lower diuresis at the end of the experiment.
Conclusions:
- Crystalloid solutions with high chloride content, such as normal saline, lower plasma pH consistent with Stewart's approach.
- The observed pH reduction is attributed to a decreased strong ion difference and progressive hemodilutional acidosis.
- The renal response to a high chloride load appears limited, contributing to the acid-base disturbances observed with normal saline.
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